Seasonal and spatial variability of hake (Merluccius merluccius L.) recruitment in the NW Mediterranean

Abstract

We studied the patterns of seasonal variability in hake recruitment by means of quarterly surveys conducted over the shelf and the upper slope of the Catalan coast (50–350m depth), with the aims of establishing the areas where hake recruitment is important throughout the year, and determining the environmental factors of the sea-floor characterising the habitat of hake recruits. In addition to sampling juvenile hake, we sampled its trophic resource (mainly suprabenthos and zooplankton) with a Macer-GIROQ sledge sampler, and we determined the characteristics of the sediment: temperature, redox potential, organic matter contents, carbonate contents and grain size. Hake juveniles were found between 60 and 160m depth in autumn and winter, while in spring and summer their depth range extended down to 300m depth. A multiple analysis of variance (MANOVA) model with interactions was used to partition the variability in hake recruits density. Season and depth stratum were the main factors accounting for the variability in hake recruitment.Well-defined nursery areas were apparent between 68 and 168m depth, but the density in nursery areaswas not different from the density in occasional nursery areas. Some sediment variables (redox potential and organic matter contents) were statistically different in nursery areas and in occasional nursery areas, indicating that juvenile hake recruit on bottoms where food resources are enhanced. The vagile macrofauna (mainly mysids and euphausiids), which constitute the main trophic resource of juvenile hake, did not overlap spatially with the main nursery areas, as they were found in higher concentrations over the 200m depth isobath. This suggests that juvenile hake and their main food resource are spatially uncoupled, at least during daytime, when both sets of samples were obtained. Establishing nursery areas for heavily exploited stocks such as hake in the Catalan sea are a valuable tool for fisheries management